It is desirable to estimate the position (or “location”) of persons and things in a geographic area with a reasonable degree of accuracy. Accurate estimations of a position can be used to speed up emergency response times, track business assets, and link a consumer to a nearby business. Various techniques are used to estimate the position of an object (e.g., a receiver). One such technique is trilateration, which is the process of using geometry to estimate a location of an object using distances traveled by different signals that are transmitted from geographically-distributed transmitters and later received at a location of the object.
In many urban terrestrial positioning systems, a “line-of-sight” signal path from a transmitter to a receiver is blocked by buildings and the like, leaving only reflected paths over which a “multipath” signal travels from the transmitter to the receiver. Using the distance of the reflected path during trilateration processing can lead to less accurate estimates of a receiver's position. However, one cannot simply ignore multipath signals that adversely affect the trilateration result without consideration of increased geometric position error associated with using only the remaining signals that may be unevenly distributed around the receiver. Thus, there is a natural tradeoff between reducing errors due to multipath and reducing errors due to poor geometry of transmitters relative to the position of a receiver.
Accordingly, there is a need for improved techniques that better account for such errors.